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Geological Magazine; March 2008; v. 145; no. 2; p. 279-294; DOI: 10.1017/S0016756807003998
© 2008 Cambridge University Press (CUP)
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Depositional origin of tuffaceous units in the Pliocene Upper Siwalik Subgroup, Jammu (India), NW Himalaya

G. M. BHAT*, S. N. KUNDAL, S. K. PANDITA and G. V. R. PRASAD

Postgraduate Department of Geology, University of Jammu, Jammu – 180 006, India

* Author for correspondence: bhatgm1{at}rediffmail.com

During late Pliocene times, extrabasinally derived acidic volcanic ashes were deposited as distal pyroclastic fallout in upland interfluvial–lacustrine settings in the northwestern part of the Siwalik basin. These ash beds occur as a bentonitized tuff band and tuffaceous mudstones in the Jammu region of India. We located and described 12 outcrops of this conspicuous, geographically widespread bentonitized tuff band and tuffaceous mudstone association at the same stratigraphic level, coincident with the Gauss–Matuyama boundary at 2.48 Ma. This bentonitized tuff band and tuffaceous mudstone association represents a stratigraphic marker horizon in the diachronous and sporadic vertebrate fauna-yielding Siwalik strata. The claystone, siltstone, and sandstone units and embedded bentonitized tuff band and tuffaceous mudstone beds represent a coarsening-upward sequence reflecting deposition in lacustrine proximal and distal bottomsets, pro-delta foresets, and mouth-bar facies capped by fluvial topsets. This study reports a chain of four contemporaneous, palaeolake basins at this stratigraphic level, which ranged in length from 2 to 7 km.

Key Words: Siwalik • Jammu India • bentonitized tuff band • marker horizon • sandy debris flow • upland interfluvial–lacustrine sedimentation






JOURNAL HOME HELP CONTACT PUBLISHER SUBSCRIBE ARCHIVE SEARCH TABLE OF CONTENTS
Copyright © 2008 by Cambridge University Press (CUP)